An aim of the study is to isolate and identify the C1 activator in anaphylactoid purpura, a disease in which, early, serum levels of C1, C4 and C2 may be reduced but C3 is spared. In diseases with comparable complement profiles, the C1 activator is either non-immune (C reactive protein combined with polysaccharide in pneumococcal disease in children) or an abnormal immunoglobulin. Possibilities for a C1 activator in anaphylactoid purpura include (1) a protease and (2) a choline phosphatide or polyelectrolyte of tissue origin combined with CRP. Attempts will be made to detect a C1 activator by measurement of hemolytic C1 before and after incubating the serum with inactive C1. If an activator is so detected, it will be isolated taking precautions to avoid artifacts due to normally oocurring protease which can activate C1 in the absence of their inhibitor. If this effort fails, CRP will be isolated from the serum and analyzed by PAGE to determine whether it might exist as a complex with a choline phosphatide or polyelectrolyte and thus eligible to be a C1 activator. A second aim will be to determine whether different modes of C1 activation in disease might be revealed by qualitative or quantitative differences in the pattern of the C1 subcomponent complexes detectable by crossed immunoelectrophoresis. Serum sources will be patients with immune complex disease including hypocomplementemic glomerulonephritis, with anaphlactoid purpura, with abnormal immunoglobulins and with pneumococcal sepsis. Free C1q as well as the beta-1 and alpha-2 complexes of C1 subcomponents, as described by Laurell, et al., will be sought. In addition, the alpha-2 complex will be measured by electroimmunoassay and the results compared with other indices of complement activation such as the levels of C4, C2 and C3 and the C4d/C4 ratio as well as with the presence of circulating immune complexes and with other laboratory and clinical evidence of disease activity. The aim will be to determine the most sensitive indicator of in vivo C1 activation and to correlate this with disease activity.